1. Field of the Invention
The present invention relates to a balancing mechanism, and more particularly it concerns a balancing mechanism which is suitable for use in balancing the arm of a robot employed in industry.
2. Description of the Prior Art
In an industrial robot, a plurality of arms are designed to balance by the inclusion of a balancing mechanism. In particular, in a robot which is operated in a playback mode so as to perform processes such as painting, welding or assembling, it is necessary for a human being to lead the robot through a desired path when teaching it, and the teaching capability can be increased if the arms of the robot are balanced at all positions along their paths.
Several types of balancing mechanisms are currently available, and one of the most simply constructed employs springs.
FIG. 4 shows a robot which incorporates a spring-type balancing mechanism, viewed from the front. Reference numeral 1 denotes a base of the robot on which a swivel slide 2 is rotatably mounted. A vertical arm 4 is pivotally mounted on a bracket 3 which is mounted on the swivel slide 2. A horizontal arm 5 is pivotally mounted on the upper part of the vertical arm 4, and has at its far end a wrist 6 having a plurality of degrees of freedom. Reference numeral 7 designates an actuator for driving the horizontal arm 5, which is disposed between the horizontal arm 5 and the bracket 3 provided on the swivel slide 2. Actuators of the swivel slide 2 and the vertical arm 4 are not shown in the Figure. A spring 8 is provided with the horizontal arm 5 so as to balance it and a spring 9 is provided with the vertical arm 4 so as to balance it and together the springs constitute a spring-type balancing mechanism.
In the above spring-type balancing mechanism, the balance of the arm changes as the inclination of the arm changes. In addition, the tension of the springs 8, 9 vary as they expand or contract. Therefore, it is practically impossible to balance the arm at all positions in its range of motion, and it loses its balance to a great degree near the end of its motion. The positioning of a heavy spring at the upper part of the arm increases its moment of inertia, which is also undesirable.